Rusty's Agility, Not Nothing

In Latin, a substance is something that stands under something else. A substance might be said to stand under its features, in the sense that they depend on it. Without Rusty, there's no Rusty's agility either. And often enough, an accident is a feature of something that it just so happens to have. Now I want to go over substance and accident again, this time giving an account that is somewhat more detailed and rigorous.